It will be appreciated that in manufacturing of boxes, especially thick corrugated boxes which may have folded thicknesses of up to 3/4 of an inch, it is important to be able to transport these box blanks through the folding, gluing, or attachment process by a transport means which maintains pressure and contact on the drive belt as the box part or blank moves with the belt. Problems of alignment and jamming occur in general when there is either insufficient pressure to maintain the box blank in frictional contact with the belt; or the rollers that are utilized to produce the top pressure become canted or otherwise inoperative as the box parts are being transported from one location to another. One particular problem with the respect to corrugated boxes as opposed to cardboard boxes is the relatively large range of thickness that have to be accommodated in order to effectuate transport, alignment and other critical parameters.
Prior art transport of corrugated boxes was accomplished in some cases by an over belt or two belt system in which there was an under belt which supported the box blank and an over belt which pressed down against the box blank, with the over belt being pressed to the under belt by springloaded top rolls. However, with the belt-on-belt system, maintainment of alignment and jam free operation is difficult because both belts must be driven. It might be thought that driving the belts simultaneously top and bottom would result in an effective transport of the box blanks. While this may be accomplished with cardboard blanks which are relatively thin, in the case of corrugated board there is belt movement in a direction transverse to the direction of travel which ends up with wave shaped curves in the to belt that in effect changes the speed of the upper belt vis-a-vis the speed of the lower belt. Therefore, in order to accommodate corrugated boxes of substantial thicknesses, adjustments of high complexity are necessitated, if this type of system is to be operated properly.
A further problem with corrugated box manufacture is that the belt-over-belt drive configuration results in belt tracking problems in which one belt affects the tracking of the other belt, with the result that one of the other of the belts comes off their respective drive pulley. In a severe case belts have to be realigned and placed on the respective pulleys as many times as three times a day, thereby cutting down production because the production has to stop in order to realign the belts. Moreover, when a belt is off track it is sometimes destroyed and must be replaced altogether, a costly factor.
As a solution to the belt-on-belt drive problem, nondriven rolls are used in direct contact with the underlying belt and/or the blank carried by the belt. Ths permits a speed differential between the top surface of the box part and the belt to be accommodated due to the non-driven nature of the rollers. Traditionally these wheels are mounted in a top frame in a fixed fashion and the frame is positioned above the belt in such a manner as to accommodate the particular boxes or box blanks to be run. This is a fixed system in which the frame carrying the ridgedly mounted rolls or wheels was adjusted for each box blank with no springloading whatsoever. The obvious problem with a fixed system is that it has to be manually adjusted each time there is a box order change. Another problem with such a fixed system is that while it works properly assuming all the rollers wear the same amount, this turns out not to be the fact such that if some rollers wear more than others then the system loses drive and the blank either folds wrong or jams in the machine, especially single thickness boxes.
In an effort to accommodate different size or thickness corrugated boxes a system was devised utilizing pairs of rollers which were pivotally-mounted and springloaded to a frame so as to be able to accommodate different thicknesses while at the same time providing continuous contact between the box part and the roller such that constant pressure was always applied to the box blank between the belt and the box blank. On regular slotted containers, the above mentioned system works satisfactorily in which only a single fold of material or single thickness of corrugated material is manipulated. But when more complicated box structure are required involving multiple thicknesses of corrugated material, in one situation the rollers would be hit so hard that they would rise up and not recontact the blank until further on down the box blank, leaving a portion of the blank with no continuous contact. Secondly, with the blank passing between the rollers and the belt at some thickness and some speeds results in rollers that cant in an almost vertical position and remain there so that only one of the two rolls ever touches the top surface of the blank. This is not self-correcting in that the pivoted double rollers in some instances remain in that configuration until physically moved back down to a horizontal double roll position. With only one pivot to the frame roll pairs, they can become permanently skewed, thereby causing the box blank and or the belt to track off completely or at least move off the direction of travel sufficient to either cause jamming or other down stream problems.